The present invention relates to an anti-locking control system of the type supplying separately regulated brake pressures to wheels on the same axle.
A system of the type to which the invention is directed includes sensors to measure the velocity or acceleration of these wheels and to generate corresponding signals, an evaluation circuit for processing these signals and generating control signals, brake pressure control devices receiving these control signals for the separate regulation of the brake pressures, and a monitoring device which separately monitors the response periods of the brake pressure control devices and, when a response period by one of the brake pressure control devices is exceeded, interrupts its control operation so that both brake pressure control devices are then operated in the same manner.
An anti-locking control system with such a monitoring device is disclosed in U.S. Pat. No. 3,883,184. In the monitoring device disclosed in that patent, the response period of the inlet valve and/or the outlet valve is monitored with the aid of a timer and if a valve being monitored has responded for too long a period of time, a signal is generated which then makes ineffective the control operation at the wheels of that axle and instead actuates, for a given second period of time, a control operation which creates alternating pressure build-ups and reductions. If the control signal continues to be present even after the period of controlled operation, the controller is permanently switched off. The actuation of the control operation before disconnection of the controller may be made dependent on the presence of certain wheel behavior factors, e.g., the presence of slip.
According to another solution described in the above-mentioned U.S. patent, the controller is normally switched off at the end of the response period unless signals derived from the wheels indicate that road conditions are the cause of the extended response period. If such signals are present, the response period is extended to another given value and only if the control signal for the brake pressure regulator is still present at the end of that period is the controller switched off and the system changed to normal brake operation.
This monitoring device does present significant advantages over a device which switches off after a fixed, given time, in that unnecessary switching off under different road conditions is avoided.